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Home , Atlantic (period), Cypress Hills (Canada), Last Glacial Maximum, Picea critchfieldii, Quaternary extinction, Sangamonian

Late of a tree in eastern

Stephen T. Jackson* and Chengyu Weng†

Department of , University of , Laramie, WY 82071

Edited by Margaret Bryan Davis, University of Minnesota, St. Paul, MN, and approved September 27, 1999 (received for review July 8, 1999) Widespread species- and -level of in been dated at 14 sites between 25,250 and 12,430 yr B.P. (16, 17). North America and occurred during the last Megafossils of temperate taxa (Quercus spp., , Acer [16,000–9,000 yr B.P. (by 14C)], a period of rapid and often abrupt sp., Carpinus caroliniana, , Carya spp., Ulmus climatic and vegetational change. These extinctions are variously americana, and Juniperus virginiana) also occur in the deposits. ascribed to environmental change and overkill by hunters. assemblages dating 24,670 to 17,530 yr B.P. indicate that By contrast, extinctions since the Middle are regional uplands were dominated by Picea, with small popula- undocumented, suggesting that plant species have been able to tions of Quercus and other hardwoods (17). The pollen assem- respond to environmental changes of the past several glacial͞ blages lack modern analogs in eastern North America (18). cycles by migration. We provide evidence from mor- Ovulate cones from the deposits were originally identified as phological studies of fossil cones and anatomical studies of fossil the species (16, 19), although this identifi- needles that a now-extinct species of (Picea critchfieldii sp. cation was questioned by some observers (20, 21). The cones nov.) was widespread in eastern North America during the Last have been variously ascribed to an extinct species (21), or an Glacial Maximum. P. critchfieldii was dominant in of the extinct variety (22) or ecotype (23) of P. glauca. We examined 45 Lower Mississippi Valley, and extended at least as as cones or cone fragments from eight Tunica Hills exposures western Georgia. P. critchfieldii disappeared during the last degla- (25,250 to 16,645 yr B.P.). Cone, scale, bract, and seed dimen- ciation, and its extinction is not directly attributable to human sions are larger than modern P. glauca, and are on different activities. Similarly widespread plant species may be at risk of allometric trajectories (Figs. 2–4). Morphometric differences ECOLOGY extinction in the face of future change. between cones of P. glauca and the fossil cones are at least as great as those between most pairs of extant North American idespread Late Quaternary species- and genus-level ex- Picea species (Table 1). Wtinctions of mammals in North America and Europe have The fossil cones cannot be assigned to any of the other extant been documented since the early 19th Century (1–4). These North American Picea species; they differ in shape, size, phyl- extinctions were concentrated during the last deglaciation lotaxy, scale size and shape, and bract size (24–30) (Table 1). [16,000 to 9,000 yr B.P. (by 14C)] (5, 6), a period of rapid and Neither are they assignable to the late Tertiary species Picea often abrupt climatic and vegetational change (7–9). In contrast banksii (31), which differs in cone shape, phyllotaxy, and bract to mammals, few Quaternary plant extinctions are documented apex-shape. We also examined 50 foliage needles and needle (10–14). Most are concentrated at the Pliocene͞Pleistocene fragments associated with the cones from six exposures (25,250 boundary (ca. 1.6 million yr ago), although a few occurred in to 17,530 yr B.P.). None were assignable to any of the extant Europe during the Early to Middle Pleistocene. No Late Qua- North American species, differing in apex shape, angularity, and ternary plant extinctions have been reported, leaving the im- hypoderm sclerification, as well as in size, continuity, and pression that few or no extinctions occurred during the last position of resin ducts (see ref. 32; Table 1; Fig. 5). glacial͞interglacial cycle. Most knowledge of Late Quaternary Cones of P. glauca and occur at other sites that vegetational and floristic change comes from fossil pollen pre- are contemporaneous with the Tunica Hills deposits (33, 34), served in and . Species extinctions may be and needles of both species are documented from contempora- masked by taxonomic smoothing in the pollen record, which neous sites to the north (C.W., S.T.J., and N. G. Miller, unpub- rarely permits species-level differentiation. Plant lished data). The occurrence in the Tunica Hills of morpholog- often support species-level identification, but few sites have been ically unique cones in association with morphologically and studied in detail, and few studies have included the detailed anatomically unique needles, and the absence of other cone or morphological and anatomical analyses required to determine needle morphotypes in the deposits indicates that they belong to whether fossil material is unequivocally assignable to extant or a single, now-extinct species, Jackson & Weng, sp. nov. extinct species. We provide evidence from morphological studies of fossil Picea critchfieldii Jackson & Weng, sp. nov.: Specific Diagnosis. Ovu- cones and anatomical studies of fossil needles for the Late late cones cylindrical, 60(?)-100 mm long, 14–20 mm diameter. of a species of Picea (spruce) that was Scale phyllotaxy 3͞5. Cone scales narrowly fan-shaped with widespread in the southeastern during, and im- rounded margins, 18–21 (12–25) mm long, 11–13.5 (7–16.5) mm mediately before, the . The organically wide; cone scale margin entire to moderately erose. Subtending preserved fossils are not assignable to any extant Picea species of bracts on cone scales spatulate, 5.5–7 (3.0–8.3) mm long, 1.5–1.8 North America; they occur at sites ranging from the Lower Mississippi Valley to the Coastal and Piedmont; and they are contemporaneous with fossils of extant eastern This paper was submitted directly (Track II) to the PNAS office. North American Picea species. Abbreviation: B.P., time before the present, as calculated by 14C. Most of the fossils are from streamcut exposures of Late *To whom reprint requests should be addressed. E-mail: [email protected]. Quaternary fluvial deposits in the Tunica Hills upland of ͞ Ј †Current address: Department of Biological Sciences, Florida Institute of Technology, Louisiana Mississippi (31°N, 91°29 W; see Fig. 1). Silts and clays Melbourne, FL 32901. accumulated in low-energy backwater pools and abandoned The publication costs of this article were defrayed in part by page charge payment. This channels (15, 16) contain abundant Picea megafossils, including article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. ovulate cones, twigs, needles, and wood (17). Picea wood has §1734 solely to indicate this fact.

PNAS ͉ November 23, 1999 ͉ vol. 96 ͉ no. 24 ͉ 13847–13852 Downloaded by guest on October 2, 2021 Fig. 1. Paleogeography of eastern North America at the time of the Last Glacial Maximum (18,000 yr B.P.). TH and BB represent Tunica Hills and Bob Black Pond, respectively, where Picea critchfieldii cones and͞or foliage occur in sediments of the Last Glacial Maximum and Farmdalian Interstadial. AC and Fig. 3. (A) Seed and seedwing of P. critchfieldii (TB-23/1093/15). (B–H) NC represent the Andersonville Claypit and Nonconnah Creek sites, respec- Representative cone scales of P. critchfieldii from Tunica Hills sediments. B–D, tively, where cones tentatively assigned to this species occur in Late Wiscon- G, and H are typical of scales from middle portions of cones. Some scales are sinan sediments. abraded or are missing small portions, and bracts are missing from some specimens. (B) PC-19/1191/8; (C) TB-23/1093/15; (D) TB-23/0393/8; (E) PC-21/ 1092/1; (F) LBS-4/1191/5; (G and H) TB-22/0293/1. (I and J) Representative cone (1.3–2.3) mm wide; bract apex rounded and minutely toothed. scales of modern P. glauca (I) Franklin Co., New York; (J) , Seeds ovate, 3.5–4.5 (2.5–5.2) mm long, 2.6–2.8 (2.0–3.4) mm ). (K and L) Representative cone scales of modern Picea chihua- wide, each with a membranous wing 8–11 (4.5–13) mm long. huana from Chihuahua, . (M and N) Representative cone scales of Needles 7–9 (4–11) mm long, 0.6–1.0 mm diameter; quadran- modern Picea breweriana from Siskiyou Co., California. (O and P) Represen- tative cone scales of modern Picea martinezii from Nuevo Le´on, Mexico.

gular in cross-section; apex acute; two resin ducts spanning entire needle length; resin ducts 60–80 (40–100) ␮m in diameter, positioned in needle angles. Holotype: University of Wyoming Quaternary Plant Ecology Laboratory collections, TB-23/1093/ 15. Paratypes: PC-19/1191/1, PC-19/1191/8, TB-23/0393/8, TB- 22/0293/1, PC-21/1092/1, PC-21/1092/2, PC-21/1092/4, LBS-1/ 0592/6, LBS-4/1191/5. Etymology: Named in honor of the late William B. Critchfield in recognition of his advocacy of under- standing the role of Quaternary history in shaping genetic structure of populations. He encouraged the senior author to investigate Quaternary spruce paleobotany and hence was partly responsible for initiating this study.

Discussion. P. critchfieldii was not restricted to the Tunica Hills (Fig. 1). Cones of similar dimension and morphology have been reported from sediments dating to 17,195 yr B.P. in western Tennessee (23), and 21,300 yr B.P. in southwestern Georgia (35) (W. B. Critchfield, personal communication, 1988; H. E. Cofer and J. Reinhardt, personal communication, 1989). We have identified needles of P. critchfieldii from sediments at Bob Black Fig. 2. Representative cones and cone fragments of P. critchfieldii from the Pond in northwestern Georgia, co-occurring with Pinus rigida Tunica Hills. (a) Holotype (TB-23/1093/15) from Tunica Bayou Site 23 (18,745 yr and Pinus banksiana during the Farmdalian interstadial (22,000– B.P.). (b) Paratype (PC-19/1191/1) from Pinckneyville Creek Site 19 (17,534 yr 21,000 yr B.P.) and with Pinus banksiana, Pinus resinosa, Pinus B.P.). (c) Apical fragment (PC-21/1092/4) from Pinckneyville Creek Site 21 strobus, and Picea glauca during the Last Glacial Maximum (21,277 yr B.P.). Entire cone was Ͼ86 mm in length; basal portion was missing. (21,000–16,500 yr B.P.). Occurrence at these sites (Fig. 1)

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Fig. 4. Cone morphology of Tunica Hills fossils (from 20 cones or fragments from 6 sites; see ref. 17) and modern Picea glauca (from 240 cones from Alaska, South Dakota, Michigan, New York, Ontario, Saskatchewan, and ). Box plots along margins portray median, quartiles, adjacent values, and outside values for the entire data sets. Upper box plots along x-axis and right-hand box plots along y-axis represent fossils, and lower box plots along x-axis and left-hand box plots along y-axis represent modern P. glauca. Scatter plots represent data for which paired values were available for the respective variables. Black dots represent fossils, and gray triangles represent modern P. glauca. Scales and attached bracts were obtained from the cone midpoint, 1͞3 of the distance from the cone apex, and 1͞3 of the distance from the cone base for each P. glauca cone. Number of scales and bracts measured from fossil cones varied from 3 to 25, depending on preservation. All were from the middle half of the cones. Seeds were removed from 12 fossil cones for measurement. Cone lengths for fossil specimens are minimum estimates in nearly all cases; most fossil cones were fragments lacking apical or basal portions.

indicates that P. critchfieldii had a range encompassing Ͼ240,000 (), and all are associated with cool (mean km2 during the Late Wisconsinan. July and January temperatures 8 to 21°C and Ϫ30 to 0°C, The youngest fossils assignable to P. critchfieldii are cones respectively) (38). An association of P. critchfieldii with temper- from the Tunica Hills (16,645 yr B.P.) and needles from Bob ate hardwoods in the Tunica Hills indicates warmer tolerances Black Pond (16,620 yr B.P.). We have found no younger fossil- than the extant species. However, its occurrence with P. glauca iferous exposures in the Tunica Hills, and the record at Bob and cool-temperate at Bob Black Pond indicates some Black Pond is truncated at ca. 15,700 yr B.P. However, P. overlap in climate response with extant Picea species. Applica- critchfieldii is the only Picea morphotype found in the Tunica tion of climate-response surface models, based on modern pollen Hills deposits, and other studies suggest that Picea persisted in assemblages, may yield erroneously low paleotemperature esti- the region to at least 12,430 yr B.P. (16). Picea populations were mates for the Last Glacial Maximum in the southeastern region absent by 10,000 yr B.P. at sites further north in the Mississippi of the United States (18). Valley (36). P. critchfieldii cones are absent from late-glacial and Pollen evidence indicates that Picea co-occurred with tem- early assemblages from deglaciated ter- perate tree taxa (Quercus, Carya, Fraxinus americana, Ulmus, rain in the mid-, where P. glauca and P. mariana cones and Ostrya͞Carpinus), Ͼ500 km south of modern interglacial are abundant (37). Evidently, P. critchfieldii never colonized populations of Picea, during the and earlier inter- these . glacial periods (39–41). These assemblages are anomalous in Paleoclimatic inferences from palynological data may be terms of modern vegetation and pollen assemblages, and have complicated by widespread occurrence of a now-extinct species been attributed to evolutionary changes in extant Picea species during the Last Glacial Maximum. Extant eastern North Amer- (42). Our results suggest that they may represent previous ican Picea species are boreal (P. glauca, P. mariana) or montane interglacial populations of P. critchfieldii, associated with many

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Table 1. Morphological and anatomical characteristics of ovulate cones and foliage needles of Picea critchfieldii and the 10 extant Picea species of North America Character P. critchfieldii P. glauca P. mariana P. rubens P. engelmannii P. pungens P. sitchensis P. breweriana P. chihuahuana P. martinezii P. mexicana

Cone shape Cylindrical Cylindrical Ovate Ovate Cylindrical Cylindrical Cylindrical Oblanceolate Cylindrical Cylindrical Cylindrical Cone length, cm >6.0–10.0 2.5–6.0 (Ϫ8.0) 1.5–2.5 (Ϫ3.5) 2.3–4.5 (Ϫ6.0) 3.0–7.0 (Ϫ8.0) 6.0–11.0 5.0–9.0 (Ϫ10.0) 6.5–11.0 6.0–17.0 11.0–15.0 5.0–6.0 Scale phyllotaxy 3/5 3/5 3/5 3/5 5/8 5/8 5/8 3/5 5/8 5/8 3/5 Scale shape Fan Fan Fan Fan Elliptic/ Elliptic/ Elliptic/ Fan Fan Kite Elliptic/ diamond diamond diamond diamond Scale length, mm 18–21 (12–25) 10–13 (5–17) 8–11 8–14 (7–15) 13–20 15–22 15–22 15–20 12–18 (10–22) 25–27 12–14 Scale width, mm 11–14 (7–17) 8–10 (4–14) 7–9 7–11 (6–12) 9–16 10–15 12–16 15–20 10–16 (7–18) 21–23 Scale 1.4–1.7 1.1–1.4 0.9–1.25 1.1–1.4 1.0–1.25 1.0–1.3 1.2–1.8 length:width (1.1–2.1) (0.8–1.9) (0.9–1.9) Bract length, mm 5–7 (3–8) 4–5 (2.5–7) 1–2 3.5–6 (3–7) 4.5–6.0 3.5–4.5 (3–5) 4.5–5.5 5.5–6.0 Bract length:scale 0.30–0.35 0.35–0.45 0.35–0.45 0.3 0.25–0.35 0.2 length (0.15–0.50) (0.25–0.60) (0.30–0.55) Seed length, mm 3.5–4.5 2.5–3.5 (2.5–5.2) (1.5–4.5) Needle apex Acute Acute Blunt Acute Blunt Acuminate Acute Blunt Acuminate Acuminate Acuminate Needle length, cm 0.4–1.3 1.1–2.3 0.6–2.0 0.8–2.5 1.2–2.9 1.4–2.7 1.3–1.9 1.4–2.2 2.0–3.0 1.1–2.8 2.5–3.1 Needle shape, Quadrangular Quadrangular Quadrangular Quadrangular Quadrangular Quadrangular Flattened Flattened Quadrangular Quadrangular Quadrangular transverse Lateral angle Acute Acute Acute Acute Acute Acute Acute Rounded Rounded Rounded Acute Resin ducts Continuous Intermittent Continuous Continuous Intermittent Intermittent Intermittent Continuous Continuous Continuous Intermittent Resin duct 70.6 ؎ 13.3 183.6 ؎ 43.6 137.0 ؎ 34.0 107.7 ؎ 18.5 244.9 ؎ 38.6 156.8 ؎ 36.8 176.8 ؎ 31.2 118.0 ؎ 17.9 52.1 Ϯ 10.4 59.1 Ϯ 16.6 250.5 ؎ 43.0 diam., ␮m Resin duct Angular Lateral Lateral Lateral Lateral Lateral/ Lateral Lateral Angular Angular Lateral position subangular Sclerified No No No No No No No No Yes Yes No hypoderm

Characters that distinguish P. critchfieldii from other species are marked in boldface. Morphological and anatomical data for extant species are from published sources (refs. 24–32) and from unpublished data. Minimum and maximum reported values are enclosed in parentheses. ako n Weng and Jackson ECOLOGY

Fig. 5. (a) Needle cross-sections for selected North American Picea species, including A, P. glauca;B,P. rubens;C,P. mariana;D,P. chihuahuana; E–G, P. critchfieldii from Tunica Hills sediments. (b) Box plots showing resin-duct diameter of selected species. (c) Box plots showing resin-duct position index for selected species. The position index is the ratio of the distance of the resin duct from the lateral angle of the needle and the distance between adjacent needle angles (32).

of the same taxa that were concurrent with it in the Tunica Hills to the dramatic environmental changes of the Late Quaternary during the Late Wisconsinan. Macrofossil studies from intergla- have consisted of continental-scale migrations (104 km) and cial sediments can test this hypothesis. changes in population density (37, 45–47). Many species have In contrast to Late Quaternary vertebrate extinctions (4, 6, alternated between abundance and rarity during the past million 43), the demise of P. critchfieldii cannot be ascribed to direct . Pinus ponderosa, which today forms extensive over exploitation by . Attribution of its extinction to a par- much of the western North American interior, was restricted to ticular event or process is difficult, especially in the absence of scattered, isolated populations during the Last Glacial Maxi- better paleobotanical data on its past geographic range and the mum (47), as were most of the temperate hardwoods now time and places of its last occurrence. Many mechanisms might dominant in eastern North America (18). Picea omorika, now be responsible, including a , failure to disperse to and restricted to small, scattered populations within a 750 km2 area colonize newly available habitat as the environment changed, or in the Balkan region, appears to have been widespread in Europe permanent or temporary disappearance of its habitat space (44). during Early Quaternary (10). Additional paleobotanical studies will help assess timing and causation of the extinction. Conclusions. Our study indicates that extinction may be another Paleoecological studies indicate that responses of plant species outcome of environmental change. Species may be at significant

Jackson and Weng PNAS ͉ November 23, 1999 ͉ vol. 96 ͉ no. 24 ͉ 13851 Downloaded by guest on October 2, 2021 risk of extinction as they respond to environmental change, (49). This extinction is potentially sobering in view of the especially when populations are reduced or fragmented by likelihood of future climatic changes, which could be of similar environmental restriction (44, 48). Although we provide here a or greater rapidity, abruptness, and magnitude as those of the clear documentation of a late Quaternary plant species extinc- last glacial͞interglacial transition (7–9, 50). tion, other extinctions may be masked by the poor taxonomic resolution of the fossil pollen record and the paucity of detailed We thank C. R. Givens for discussion and field assistance. Lab and field morphological studies of plant macrofossils. The late Quaternary assistance was provided by K. Anderson, D. Boone, L. Lobaugh, J. Kearsley, M. Scherr, S. Stewart, B. Strauss, and C. Van Kirk. J. L. disappearance of P. critchfieldii, after several thousand years of Betancourt, G. K. Brown, R. L. Hartman, B. Huntley, H. Iltis, J. T. dominance in the Lower Mississippi Valley and widespread Overpeck, T. Webb, III, and W. A. Watts provided discussion and occurrence in the unglaciated southeastern United States, un- encouragement. This study was supported by the National Science derscores the notion that ‘‘no species is safe’’ from extinction Foundation Climate Dynamics and Ecology Programs.

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